This little guitar amp, that had been used for a PA system
with a
dynamic microphone, started picking up the radio station at one
location it was used, and has a significant amount of background noise.
It might be fixable, but probably not by me.
What to do?
In looking for new portable PA systems, I didn't find anything that
appeared like it would produce quality sound, was adequately portable,
and also cheap. This
Audio Choice C100 system looks nice, but is rather large and
heavy, and I couldn't find the manufacturer's web site, which makes me
wonder if it is still in production. This
Peavey Messenger looks nice, has all the desired features, is
nicely portable (although a little heavy at 20+ pounds) but at $500 was
a bit expensive for my blood. Earlier models of the Roving Rostrum
have demonstrated themselves to be rugged, reliable, easy to set up,
with long battery life, and mediocre but adequate sound quality.
Perhaps these newer models have better sound quality, and
they did up the power rating from 35 to 50 Watts, but for $700, even
the Peavey looked like a better deal. This
portable Karaoke machine seems to come in at least a
couple models with different power ratings, 10 Watt, and maybe 30
Watt, but it looks like cheap plastic junk. And it
is hard to find technical specs on the audio quality for some of these
units, too. Fender
has some nice looking units, but early models had poor quality
speakers, and the larger units are quite heavy to carry around. Newer
models claim to have better speakers, and hopefully
they do. Prices from $400 and up for the larger
units put me off, and while the smaller systems are really cute, they
only have one speaker, although that makes things simpler and the
system being replaced also only has one speaker. Pricing for the P10 is
about $200, so it might be competitive. Given that the bigger
units initially had poor quality speakers, though, it made me a little
shy about their smaller unit with only one speaker.
Aha?
About that time, I read a review in PC Magazine for Portable
Speakers with Power. While some of the units
sounded interesting, many seemed to have drawbacks for use as a
portable PA system component. None of the units have a microphone input
of any sort... some have only an iPod docking port, although most have
a "line level" input also. In the review of their favorite
unit, the Altec Lansing, they referred to an earlier review of another
item which seemed quite interesting, the 40 Watt Virgin
Electronics Boomtube EX, to which they had also given an
Editors Choice award. While they considered it pricey, the prices have
apparently come down since that review back in Feb 2005, as Amazon
has it for much less than list price.
The problem with the Boomtube and competitive devices for PA
system use
is their lack of
microphone inputs. So I went shopping for a portable preamp.
Many such exist, but most of them are either in the several
hundred dollar range, or else seem to aimed at using micro stereo
microphones. After extensive searching, I discovered the Applied
Research and Technology MicroMIX, which is much
cheaper at
B&H and elsewhere. While out of the box it
requires AC power, the wall wart converts that to 12V DC 150 mA, so a
small battery pack could probably be made to work with it.
You'd need to find a power connector with 2.5 mm inner
diameter, and 5 mm outer diameter to hook it up.
What I did
I had a preamp/mixer and some microphones on hand for testing, so I
decided to obtain the Boomtube EX and see how it sounded. Initial
testing at home was positive, so I took it to a small
gathering, and did a "head-to-head" comparison with an old Roving
Rostrum. Everyone unanimously voted as preferring the
Boomtube. So then I went ahead and ordered the ART MicroMIX. It also
sounded good in home testing, and I used it the next
week at a similar gathering, again with positive results.
Someone
there noticed that my 1/4" to 1/8" adapter wasn't
stereo, and that all my positive results had been gathered with only
one active channel. Now when I'd first found and used that
adapter during initial setup, the thought crossed my mind that it might
not be sufficient for converting mono to stereo input, but I wanted to
hear the quality, and only had a mono signal anyway, and then I kind of
forgot about it. But now I had another problem... too many
wires, and too many parts... see the boomtube in the background, the
MicroMIX is almost obscured by the mike wire, and there are two wall
warts plugged into the extension cord.
So I figured, hey, let's jam all this stuff into a project
box.... just
check Radio Shack
to find the right size... I figured I needed something 10-12"
long, 4-6" wide, and 2.5-4" high, so that I could cram the MicroMIX,
both wall warts and the end of an
extension cord into the box, including rolls of wire from the wall
warts to the MicroMIX and the boomtube, and still have room to mount a
microphone jack..... oops, they have nothing that big. Not
even close! Back to a broader internet search, and I found
nothing. I remembered a friend had made a nice laptop
carrying case out of some sort of plastic, and I thought I'd see him
again soon and would ask again for the details of how he did it. On the
way to the place where I figured I'd see him, I passed
the Fry's on Hamilton Avenue in Campbell, CA. With a little time to
spare in my schedule, I ran in to see if they had project boxes... and
indeed they did, on aisle 8B. And
they had a much greater variety than Radio Shack! Including
one that fit my dimensions at the small end: 10x4x2.5". I'd
sort of hoped to find something with at least one dimension bigger than
my minimums to be sure everything would fit, but it was that or
nothing, so I bought it. It is an LBM #144
by LMB Heeger Inc, 6446 Flotilla St, Commerce CA. They have a
variety of sizes, but their biggest of that style seems to be the one I
found. The do have bigger ones in their Flangelock style of
chassis boxes.
So now I had to actually do some skilled assembly work, to
avoid which is why I've done software for my whole career in
spite of having a EE degree... Actually, the EE part wasn't
too bad... I do still have a soldering iron that a former neighbor gave
to me, was able to locate the solder, and the clamp jig for holding the
parts! The two electrical parts to be fabricated were both
wires. The source for both wires was a right-angle male to
right-angle male
short "jumper" wire that I had on hand. That way, one end of
each wire
was already done, and the right-angle connectors allowed the project
box to be only 4" wide. Straight connectors would have required another
inch or two of width in the project box.
One was an extension wire for the microphone input, so that
the
microphone jack could be on the same side of the project box as the
volume controls (the MicroMix has them on opposite sides, but it is
smaller, so it has to). Radio Shack did have the mountable
1/4" phono jack (but I had to buy a pair), and some grommets to protect
wires passing through holes in the box (I had to buy a whole assortment
pack, but they were cheap). I planned to put the new
microphone jack to the right of the MicroMIX in the project box, so
that its open wires would be mostly surrounded by metal of the MicroMIX
or the project box walls. Although I did also put electrical
tape on those nearby metal surfaces to avoid shorting things out. That
is just because I really, really don't want to open up
the box again once it is made; there was adequate clearance that no
shorts should occur even without the tape. The second wire
was for the audio output. As shown below right, this had to
include a "conversion" from mono to stereo, so you see that the center
wire is soldereded to both the left and right channel connectors.
Now for the box modifications. While it would have been nice
to have had a drill press, I'd have to do a lot more work to justify
having one, and I don't plan to do that much. So here were
the major tools:
I'd strongly recommend that anyone that might try to
duplicate my
efforts would do two things I didn't. Not doing them really doesn't
save time. First, there are 4 items on the front of the
MicroMIX: power indicator LED (green), Phantom Power pushbutton switch,
Phantom Power indicator LED (red), and the input GAIN control (rotating
knob). At first I thought I'd cut out a big section so you
could see the face, but the legends were on the top of the MicroMIX box
so there was little benefit to reducing the strength of the box that
much... 4 drilled holes would expose everything that needed to be
exposed. And then a 5th hole for the 1/4" in mike jack to the
right. So what I should have done was make a paper template
to position those four items, placed it on the face of the MicroMIX,
and measured it to the top of the wall of the box. And then
transferred it to the outside of the box, and drilled through the
template. And the second thing is that I should have found a
block of wood to sit inside the box, so that when the drill bits got
through the metal, they'd have the wood to sink their teeth into,
instead of bouncing around and making the holes more triangular than
round... the jaws on the vise weren't big enough to hold the
top of the box in the middle, because the bottom of the box got in the
way, so I could only clamp the end, and drill several inches away.
Having a chunk of wood in the box would have made the
clamping easier too. Did I mention it would have been nice to have a
drill press? Anyway, I got some holes drilled, and the little
diamond grinder you see in the Dremel tool above was a lifesaver in
cleaning the edges of the holes, and making them round again, and
adjusting the hole for the GAIN knob until it would actually fit....
Oh, and that other bit in the Dremel picture came in real
handy for the
slot on the left edge of the box for the power wire. Because
both ends of the extension cord were molded, large, and I didn't want
to cut it and mount power plugs on the project box, both for space and
time reasons, and I didn't want to cut a hole big enough for the end of
the extension cord to pass through, a slot at the edge, complete with
grommet, seemed the most appropriate solution. The other bit
is a "rotary saw" bit, which I had bought when I happened to see them
available, because it looked like a "neat accessory" for the Dremel.
Sometimes those impulse buys pay off! It was the perfect bit
for the job. There was also a similar need for a slot in the
top of the box, through which could pass both the 12V pulsed DC output
of the boomtube's wall wart, and the output signal from the MicroMIX to
the boomtube.
Note the two coils of wire in the picture above, inside the
box (and
tied with wire twisties). To avoid making an inductor out of
coils of wire, and picking up all sorts of in appropriate RFI noise
from the atmosphere, it is good to place both ends of the coil
together, and then coil both wires of the resulting loop together. That
way the signal picked up in one winding is counteracted
by the signal in the other winding, which is going the opposite
direction (with respect to the flow of the main signal through the
wire). This is similar to the theory of how balanced audio
signals work. Now being in an aluminum box helps avoid RFI
noise too, but there is another reason to wind the coil in this
manner... to avoid generating magnetic fields of our own, which could
get picked up at the other end of the box by the unbalanced microphone
wire. Oh, and if you ever want to uncoil the wire again, it
turns out that you can avoid tangles by starting at the loop, and
shaking the rest of the wire free. Keep that in mind when
winding up loose external cables like microphone or speaker wires.
The final modifications to the box were four slots in the top
so that
the boomtube can be strapped to the project box. The boomtube
didn't come with any mounting brackets, so straps seemed more
appropriate than drilling holes through the case and whatever important
stuff happened to be inside right there... and I didn't want to take it
apart, after all it is brand new and still under warranty! So
a couple industrial strength plastic ZIP ties, having abouth the same
width as some of the trim pieces on the boomtube, don't look too bad,
and I hid the ends of the ZIP ties inside the project box. Here is what
the audience sees:
All smooth aluminum, the rectangular base, and the
cylindrical top,
plus the two detached tweeters.
And the speaker/operator sees basically the same thing, but
with all
the wires and controls.
Here's another shot, showing all the controls a little
closer, and the
connections to the boomtube.
Notice how the power wire (left) and audio input (right)
wires to the
boomtube come from the grommeted slot in the top of the box. The two
middle wires are standard RCA plug speaker wires. The ones that came
with the boomtube are only 3' long, but
longer ones can be obtained if desired. I did stick labels on
all the controls and connections after I took this picture. The
microphone is plugged in, in these pictures. It
is one I bought from DAK for $20 nearly 20 years ago, and they are
great little electret microphones, running on one AA battery. I'd be
glad to learn about any equivalent, inexpensive
imcrophone available on the market today (here's a scan of the microphone specs).
So in the end, a bunch of messy
stuff got hidden, and there are 2
speaker wires, one power wire, and one microphone and wire, plus the PA
package itself. It can be neatly packed into an ancient soft-side
briefcase someone threw away at our house some years ago.
My out-of-pocket costs were $141, and I used a few items I
had on hand
shielded 1/4" right-angled phono wire
2
lamp extension cords
DAK microphone
2
industrial strength ZIP ties
The total cost, then, is probably about $180, about the cost
of some of
the lower end PA systems. In putting this page together, I notice that
Amazon has reduced the price of the boomtube EX by $10 since I bought
this one! It is a neat little unit, with good sound quality. You could
use it as laptop speakers for your computer, for your portable CD or
MP3 player, or you could do what I did, and make a portable PA system
that has better audio quality than most price competitive units. Maybe
I'll get another unit for use with the laptop.
Alternate solution
After I was mostly done with the above project, someone pointed out the
Roland
Micro-CUBE. This item would be nearly a direct
replacement for the original Guaytone, but is fairly low power (the
Guayatone doesn't have a rating plate, and is too old to be found
on-line, so it is hard to compare). For use as a PA system,
one would need to keep the effects turned off! The person
that brought this device to my attention thought that it might prove
adequate for groups of 50 people in a room with average acoustics. It
is cheap, light, battery operated, easy to set up, and
appears rugged. Reviews on the internet are mostly positive,
although many speak of it being low-power (2 Watts). P.S.
The someone that pointed out the Roland unit is now a happy Boomtube EX
user! Know anyone that wants a Roland? LOL
Problem
Someone
there noticed that my 1/4" to 1/8" adapter wasn't
stereo, and that all my positive results had been gathered with only
one active channel. Now when I'd first found and used that
adapter during initial setup, the thought crossed my mind that it might
not be sufficient for converting mono to stereo input, but I wanted to
hear the quality, and only had a mono signal anyway, and then I kind of
forgot about it. But now I had another problem... too many
wires, and too many parts... see the boomtube in the background, the
MicroMIX is almost obscured by the mike wire, and there are two wall
warts plugged into the extension cord.
And
they had a much greater variety than Radio Shack! Including
one that fit my dimensions at the small end: 10x4x2.5". I'd
sort of hoped to find something with at least one dimension bigger than
my minimums to be sure everything would fit, but it was that or
nothing, so I bought it. It is an LBM #144
by LMB Heeger Inc, 6446 Flotilla St, Commerce CA. They have a
variety of sizes, but their biggest of that style seems to be the one I
found. The do have bigger ones in their Flangelock style of
chassis boxes.
So
in the end, a bunch of messy
stuff got hidden, and there are 2
speaker wires, one power wire, and one microphone and wire, plus the PA
package itself. It can be neatly packed into an ancient soft-side
briefcase someone threw away at our house some years ago.